Power semiconductor modules are devices for converting and controlling the flow of electric energy and are used as inverters, DC/DC converters, and other power conversion devices. Power semiconductor modules are widely used in homes, industries, automobiles, aircraft, wherever power must be converted or controlled. Power semiconductor devices, including diodes, thyristors, power MOSFETS and IGBTs, are typically assembled to form power semiconductor modules, which may contain several such power semiconductor devices.
Controlling and converting power in power semiconductor devices of the type described above produces significant heat. This heat will increase the temperature of the power semiconductor module to the point of failure of the power semiconductor devices. Therefore, efficient heat management is a main requirement for electrical equipment using power semiconductor devices of this type. For this reason, power semiconductor devices used in typical applications like aircraft power conversion typically are based on silicon carbide SiC which has better thermal characteristics than mere silicon based power devices. SiC based power devices may operate up to temperatures as high as 250° C. and produce less heat than corresponding silicon based devices. However, even for SiC based power devices efficient transfer of heat away from the semiconductor device is a main requirement.
US 2011/0128707 A1 discloses a power semiconductor module suitable for power conversion on aircraft. In this power module, heat producing SiC power semiconductor devices, like MOSFET or IGBT, are mounted to a substrate using Chip on Board technology. The power semiconductor module includes an insulating substrate with a conductive circuit layer attached to one side. Power semiconductor devices are attached to the conductive circuit layer by soldering. The power semiconductor devices are wire bonded to each other and to the conductive circuit layer to form a power conversion circuit. The power semiconductor devices as well as the wire bonds are embedded in a soft casting “Globtop” compound protecting the circuitry and preventing short circuiting of the wire bonds. A base plate is attached the side of the insulating substrate opposing the power semiconductor devices. Heat generated in the power semiconductor devices by the power conversion is conducted away from the power semiconductor devices first through the conductive circuit layer, then through the insulating substrate, to the baseplate which dissipates the heat by thermal contact with a heat transfer fluid, e.g. air.
DE 10 2011 083 223 A1 describes another power semiconductor module suitable for power conversion by bridge circuits including MOSFETs or IGBTs. The power semiconductor module is made up of two printed circuit boards each including an insulating substrate layer sandwiched in between an upper metallization layer and a lower metallization layer. The two printed circuit boards are vertically stacked upon each other with a gap formed in between the lower metallization layer of the upper board and the upper metallization layer of the lower board. A power semiconductor chip is disposed in the gap and is electrically conductively connected to the metallization layers.
While the Globtop configuration described in US 2011/0128707 A1 provides for sufficiently effective heat dissipation in a number of applications, it requires considerable mounting space and is prone to failures, particular with respect to the wire bonds. Moreover, testing for failures can be done after final assembly of the power module only, i.e. in a situation where wire bonding has been finished and the components are embedded by the Globtop casting. The configuration shown in DE 10 2011 083 223 A1 avoids a number of wire bonds, but requires relatively sophisticated handling of the printed circuit boards to position the semiconductor chip precisely in the gap. Moreover, the power semiconductor module still requires significant space.
Therefore, it would be beneficial to have an improved configuration for a power semiconductor module allowing more efficient assembly and/or better utilization of space while still providing sufficient heat dissipation capability.